Method and apparatus for fabrication of articles by molten and semi-molten deposition

ABSTRACT

A method and apparatus for depositing metals and metal-like substances in two and three dimensional form without a substrate in a safe, rapid and economical fashion using gas shielded arc welding equipment and programmable robotic motion. The method and apparatus includes the use and application of robotic controls, temperature and position feedback, single and multiple material feeds, and semi liquid deposition thereby creating near net shape parts particularly well suited to rapid prototyping and lower volume production.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/518,121, filed Oct. 20, 2014 entitled “Methodand Apparatus for Fabrication of Articles by Molten and Semi-moltenDeposition” which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/892,526 entitled “Method and Apparatus forFabrication of Articles by Molten and Semi-molten Deposition”, filedOct. 18, 2013, the disclosures of which are herein incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to equipment and processes used for thefabrication of parts by depositing layers of metallic material, commonlyreferred to as additive manufacturing, and more particularly toequipment and processes which fabricate metallic items formerly made byprocesses such as casting, welding, subtractive machining, and forging,and generally does so without the need for specialized tooling and longlead times associated with these manufacturing processes.

BACKGROUND OF THE INVENTION

Fabrication of three-dimensional metal articles by deposition ofsuccessive layers of metallic powder or weld beads, where the layers areheat bonded together to build the object, is well known in the field.

Processes using plasma or laser fused deposited metals have been usedfor many years to produce a layered structure on a substrate, but aretypically very energy intensive and extremely slow. The requiredequipment is expensive to purchase and operate as a high energy plasmagenerator is needed to vaporize the powder stream or high energy laserbeam is needed to generate the melt-pool on the growth surface.

Similarly, processes using energetic wire deposition enable the rapidprototyping and manufacture of fully dense, near-net shape components ona substrate. However, the deposition must be done slowly to allow eachlayer to cool prior to the next layer being added. In addition, theresulting items produced by these deposition methods often require theremoval of the substrate as a secondary operation, which can increasethe cost, destroys the substrate when being removed, can damage theobject from which the substrate is being removed, or require carefulengineering to incorporate the substrate into the structure of the itembeing manufactured, thereby limiting the configurations that can beproduced.

The bonded layers from these current processes are sometimes milled to afinal shape either after each layer is formed, or after all layers havebeen made. Those knowledgeable in the art accept that parts fabricatedusing this welding method, are either small—due to the large amount ofheat inputted through the welding process- or extremely expensive due tothe long time needed to fabricate them.

Sintered metal processes use powdered materials and a high power laserbeam to selectively melt the powdered material, layer upon layer.Although relatively accurate, these processes are also slow and requirea high temperature post processing operation to obtain a usable part.Even after post processing, the resulting part has the physicalproperties of a sintered metal part rather than being homogeneous.Furthermore, post processing can result in significant distortion andthe required equipment is expensive. Laser melting of powered materialscan be used and thus eliminate the need for oven post heating, but areeven slower due to the increased heat.

These processes used to fabricate three dimensional metallic items byadding layers of material have many disadvantages. Similarly, processessuch as casting and forging require large investments in tooling andequipment and thus fundamentally suited only for large volume productionprocesses such as welding are generally labor intensive, require highlyskilled personnel and require a great deal of pre-assembly preparationand post assembly finishing. In addition, these processes typicallyrequire long periods of time to complete the production of a single partdue to all the drawings and preparation required for the individualcomponents. What is needed, therefore, is a method and apparatus toreduce the amount of capital equipment investment, process expense, andtime needed to fabricate a 3 dimensional part, including the amount oftime needed to form the part and the amount of time to finish the partfor final use.

SUMMARY OF THE INVENTION

A method of and apparatus for depositing metals and metal-likesubstances in three dimensional form in a rapid and economical fashionis herein disclosed, such that the new process satisfies an unmet needof single and smaller volume production in creating near-net shapeparts, and providing an avenue to limited production heretoforeunavailable, while not precluding its use in large volume production aswell. As described herein, the new process of the present invention canform a metal part or a metal-like part comprising a composite includinga metallic material, a combination of different metallic materials, aceramic material, and components of various other materials.

The present invention uses modified gas shielded arc welding equipmentreferred to as GMAW (Gaseous Metallic Arc Welding) and also known as MIG(Metallic Inert Gas). It can also use TIG (Tungsten Inert Gas) processesand apparatus in the same embodiment. The MIG or TIG welding torch ismounted onto a multiple axis robotic mechanism to automatically depositone or more metals in layers according to the part design whilesimultaneously heating or cooling the resulting built-up structure toachieve a faster deposition of material and to maintain and improvedimensional accuracy.

The metal-like part exhibits some metallic properties while not beingentirely made of a metal. In one embodiment, the metal-like material isprovided as a feedstock by enclosing the non-metallic components withina tube of metal. While some currently known MIG welding wire uses a tubeof metal surrounding a flux core, a metal-like feedstock as used herein,in one embodiment, includes a tube of metal having a core other than aflux core.

In addition, a method is disclosed whereby a metallic three dimensionalitem is produced without the need of being permanently attached to apreform or substrate during the manufacturing process. The resultingpart does not require removal of a difficult to remove substrate, toprovide a near-net shape part requiring no further removal of structure.

The present invention provides, in different embodiments, an object,part or item which does not include a permanently attached base orsubstrate. As discussed herein, the build table upon which the object isformed is removably adhered to the object, such that the object remainsfixed to the build table during forming of the part, but is removablefrom the build table without significantly altering the form of eitherthe part or the build table. Consequently, the build table is reusableto form additional objects of the same or different sizes or differentdesigns.

In one or more embodiments of the present invention, there is provided amethod and apparatus to rapidly produce one or more parts to be used inplace of castings, weldments, and forgings, while eliminating the needfor tooling or molds to produce the part.

In one or more embodiments of the present invention, there is provided amethod and apparatus to provide a near net shape part with optimumdimensional accuracy. As used herein, a near net part is a part producedby a manufacturing process which is close to a finished part. The nearnet shape part requires a minimal amount of after-part finishingprocessing typically a limited and controlled material removal processand polishing, if necessary.

In one or more embodiments of the present invention, there is provided amethod and apparatus configured to control the built in stresses in thepart, so that the desired physical material properties of the part areobtained.

In one or more embodiments of the present invention, there is provided amethod and apparatus configured to control the grain structure of thematerial in the part, so that the desired physical material propertiesof the part are obtained. In one or more embodiments, a submergeddeposition process takes place below the top surface of the quenchantwhich provides properly controlled parameters, wherein the quenchantfluid and decomposition byproducts are excluded from the hot zoneprimarily by the action of mechanical shielding, shield gas, anddeposition byproduct outflow. An inverted process allows gravity toassist in shielding the hot zone.

In one or more embodiments, a means of determining the temperature ofthe quenchant at a predetermined distance from the part as a means oftemperature direction and control is provided. Such means of monitoringtemperature includes optical monitoring or sensor based monitoring.

In one or more embodiments of the present invention, there is provided amethod and apparatus configured to control and prevent an outflow ofmolten material from a hot zone wherein material is being deposited in adeposition, or hot zone, where the material is still molten orsemi-molten.

In one or more embodiments of the present invention, there is provided amethod and apparatus configured to control and prevent a plastic flow orsag of deposited material in and adjacent to the hot zone.

In one embodiment, the part is deposited layer by layer on a build tableof copper, copper clad, or other suitable metallic material to providethe electrically conductive surface. In a second embodiment, thedeposition is made using at least two wires of differing polarities toallow for the initial layer to be deposited on either a platen ofmetallic surface or a non-metallic surface such as a ceramic table. Theuse of the two wire approach also minimizes the heat input to thestructure being fabricated and the energy needed to produce it. Thisreduced energy input allows the part to be fabricated more quickly. Inthis two wire embodiment, the material is deposited in a range oftemperatures that include the material's temperature in plasma, moltenand semi-molten states.

Generally, the semi-molten state is used during a first pass in order toproduce a continuous initial deposition surface or trace partiallyadhering to the surface of the platen, such adhesion being sufficient toprevent lifting of said trace during subsequent passes, but insufficientto preclude easy removal of the completed item or part, said adhesionbeing achieved by adjustment of deposition parameters and selection ofsuitable platen materials for the type materials being deposited.Suitable platen materials include heat resistant conductive andnon-conductive materials and are capable of being temperature controlledby the quenchant fluid.

In different embodiments, the deposition process benefits from a lightdusting of a metallic powder on the surface of the platen to ensureelectrical conduction.

In one or more embodiments of the present invention, there is provided amethod and apparatus configured to provide a safe environment for anoperator and to control the unrestricted discharge of processbyproducts. Byproducts are removed and processed by conventional meansif desired, as is well known in the field of welding and othermanufacturing processes.

In one or more embodiments, a gas sensor is provided to monitor thepresence of undesired atmospheric or by product gasses, as well as ameans for controlling the influx of additional shield gasses to excludethe atmospheric or by product gasses from the deposition zone.

In different embodiments, computer controls are integrated into theother process controls, as is known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the major components and subassemblies of afabrication system.

FIG. 2. illustrates a deposition nozzle module of the present invention.

FIG. 3. illustrates a prototype part made by an embodiment of thepresent invention.

FIG. 4. illustrates a two wire deposition device of the presentinvention.

FIG. 5. illustrates an alternative two wire deposition device of thepresent invention.

FIG. 6 illustrates another embodiment of a portion of a fabricationsystem.

FIG. 7 illustrates an underneath perspective view of a platen assembly.

FIG. 8 illustrates a top perspective view of a platen assembly includingdeposition of material.

FIG. 9 illustrates a side view of a nozzle head fixture and a nozzleassembly.

FIG. 10 illustrates a back view of a nozzle head fixture and a dockednozzle assembly.

FIG. 11 illustrates a front perspective view of a nozzle head fixtureand a docked nozzle assembly.

FIG. 12 illustrates a perspective view of a part being formed with apart fixture.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to the fabrication of an object usingthree-dimensional computer models and computer numerical control (CNC)robotics to control the position of the application of a metal ormetal-like deposit. The present invention is directed to form ametal-based or metallic two or three dimensional object, as contrastedwith known three dimensional plastic printing technologies in use todayfor providing objects made of plastic. The fabrication of these objectsformed of metal does not require the use expensive tooling or molds.Additionally, the present invention is particularly well suited to rapidprototyping and lower volume production of metallic parts.

The preferred embodiment of the apparatus includes an inert gas arcnozzle fed with wire and gas, a non-stick build surface mounted to amoving table, a multi-axis robotic actuators, a master controller,sensors, a tank full of quenchant, an enclosure, and an air filteringsystem.

At least one distance sensor, or alternatively, electronic arc lengthsensing, as currently employed by welding manufacturers such as Lincoln,Fronius, Miller, ESAB etc, continuously monitors the height of thepreviously deposited metallic layer and compares the actual height ofthe pervious layer to the specified height. If any section of the layeris lower than specified, the system can go back and fill it prior tostarting the new layer, or the speed of deposition can be modified todeposit additional material at the low section.

A temperature monitoring means and simultaneous partial submersion ofthe part in a bath of quenchant fluid while building layers is used toheat or cool the part as each new layer is deposited in the preferredembodiment. This feature allows control of built in stresses as well asmanipulation of the final grain structure and material properties. Thesupplemental control of part temperature, near but not coincident withthe hot zone of the deposition, provides fine control of itemcharacteristics including the ability to prevent outflow of depositedmaterial from the vicinity of the hot zone and to preclude plastic flowor sag adjacent to the hot zone. In addition, submersion in a bath ofquenchant fluid is the preferred method of heat control over a spray ora quenchant cascade, as liquid does not remain on the surface to whichmaterial is being deposited during the next pass nor is liquidintroduced into the hot zone. Consequently, the risk of steam, hydrogenand oxygen production which can cause embrittlement or porosity isthereby reduced or eliminated.

The present invention provides a safe environment for the operator andcontrols the unrestricted discharge of process byproducts by providingan enclosure to trap toxic fumes generated during the depositionprocess. The enclosure also retains the inert gas used to shield thewelding arc from undesired atmospheric gases, so that less inert gas isneeded. In addition, the inert gas within the enclosure, in differentembodiments, is purged and reused for the next part.

As depicted in FIG. 1, a fabrication system 1 includes a Build Table 5acting as a support for the part being fabricated. The Build Table 5 issupported by Build Table Supports 6 and is raised or lowered by way ofBuild Table Height Actuators 7 into a bath of quenchant Fluid 10, whichis contained in a tank 11. As illustrated, the actuators 7 are locatedoutside the quenchant fluid 10 and the tank 11 such that the actuatorand the support are not immersed in the fluid. In this embodiment, theactuators 7 are located within an enclosure 40. The temperature of thequenchant Fluid 10 is maintained by a Temperature Control Unit 12. Aquenchant Level 15 is maintained at a monitored, fixed position so thatthe Build Table 5 and a portion of the fabricated part are cooled orheated, as discussed herein. As used herein, the term “build” is used torefer to a part being produced or “built”. In the preferred embodiment,the quenchant fluid 10 includes a quenchant configured to cool theobject being formed on the build table 5.

A multi-axis Robotic Actuator System 20 is positioned above the BuildTable 5. The Robotic Actuator System 20 includes at least one Z AxisActuator 21 which moves a Z Axis Rod 25 vertically, as illustrated,relative to the Build Table 5. A Deposition Nozzle Module 30 is attachedto the end of the Z Axis Rod 25 and is connected to a Deposition PowerSupply 35 and a supply of Inert Gas 36 by way of a Welding Tether 37.The described welding and deposition equipment is familiar to thoseknowledgeable in MIG or TIG welding processes, but modified to delivermuch lower power and very different waveforms than typically used forwelding applications. The inert gas 36 is also known as a shield gas.

The Build Table 5, bath of quenchant Fluid 10, Robotic Actuator System20, and Deposition Nozzle Module 30 are all contained within anEnclosure 40. The Enclosure 40 creates a controlled, Enclosed Space 45for the process and in the preferred embodiment is isolated from outsidetemperature variations and air currents. The inert gas is containedwithin the Enclosed Space 45 and maintained at a desired Inert Gas Level46, thus minimizing the chance of contamination of the material beingdeposited to form the part. While the inert gas level 46 is shown as aclearly defined gas level, this level is for illustrative purposes only.During operation of the system 1, the gases present in the enclosure 40intermix, with the level of shield gas being determined by theconcentration of the mixture rather than a physical level as shown.

The byproducts generated by the process are also contained in theEnclosed Space 45 and in the preferred embodiment are vented by way of aVent Fan 47 to appropriate filters, scrubbers or environmental controlsin order to ensure operator safety. An oxygen sensor 48 is operativelyconnected to the controller 50 to monitor and control the level ofoxygen gas within the chamber. If the chamber is determined to have toomuch oxygen gas, or not enough inert gas, the controller 50 delays thestart of the deposition process or turns off the system, so that repairsor adjustments can be made.

In another embodiment, the sensor 48 is used to provide for a reductionof shield gas during material deposition. The higher the concentrationof shield gas in the chamber, the lower the requirement for shield gasinput at the nozzle. Initially the chamber contains normal air, withthat air being excluded from the deposition zone by the shield gas beinginput present at the nozzle. In other optional operating settings,normal air is completely removed from the chamber and the chamber isfilled with a shield gas before beginning the formation of the part.

In the preferred embodiment, the enclosure 40 is a sealed container inwhich an inert gas, such as carbon dioxide, or argon, or a selected mixof inert gases is used in the part forming process. The enclosure 40 iscoupled to a gas circulation system (not shown) as would be understoodby those skilled in the art. The inert gas, such as carbon dioxide andargon are removed and trapped from the air and reused in the enclosure40.

A central Computer Controller 50 is connected to all subassemblies ofthe apparatus by means of a Temperature Control Cable 53, a RoboticControl Cable 54, and a Deposition Power Supply Control Cable 55. TheComputer Controller 50 has master control over each of the subsystemsalong with control over the entire process, as described below.

As depicted in FIG. 2, the Deposition Nozzle Module 30 incorporates aHolding Device 61 for securing a Deposition Nozzle Assembly 63 as wellas the Welding Tether 37. A Part Temperature Sensor 66, an ElectronicHeight Gauge 67, and a Gas Monitoring Probe 68 are also mounted to theDeposition Nozzle Module 30 so that all supported components remain inthe same relational position as they move together. These sensors areconnected to the Computer Controller 50 by way of a Nozzle Module cable69. It is important to note that the Part Temperature Sensor 66 ispositioned and oriented so that it can accurately measure thetemperature of the part at some preset distance between the top of thepart, where the new materials layer is being deposited, and the buildtable or quenchant Level 15.

The Electronic height gauge 67 determines if any areas of the part arelower than desired. Optionally, in one or more embodiments, additionalheight sensors are mounted to ensure that the top of the part is in thecorrect position as determined by the height of the build table 5 withrespect to the nozzle module 30.

It is known in the art that the Robotic Actuator System 20, in differentembodiments, include multiple axes and thus allow manipulation of morethan one Deposition Nozzle Module 30. Multiple Deposition Nozzle Modules30 allow for faster deposition rates or deposition of two materials atthe same time. In the preferred embodiment where the nozzle assembly 63incorporates a MIG welding head, the welding head is inputting heatduring formation of the part with up to 7,000 watts of power.

The typical Direction of Travel 70 for the Deposition Nozzle Module 30is depicted. An angular orientation 71 of the nozzle relative to thepart is employed for the purposes of maximizing deposition rate andminimizing heat buildup while narrowing the spread of the depositedmaterial. This angular orientation 71 is not an essential element of theinvention, but is shown for clarity and as an illustration ofestablished practice. In this case, an additional rotational elementwould be added to the nozzle as is already common in the art to enableomnidirectional movement. In the preferred embodiment, feed wire is usedto provide material for the build-up of the item being produced, and thewire discharge means can be a MIG nozzle, TIG feed wire dispenser, orany similar means available to the art. Feed wire is preferred overpowdered metal for cost, environmental, and safety reasons.

The sample part 80 depicted in FIG. 3 was made without use of thequenchant Fluid 10. The uneven Top Surface 81 of this sample part, whichincludes sag 82, illustrates how improper cooling results in a partwhich lacks dimensional stability during fabrication and which includesunwanted defects. The teachings of the present disclosure, in contrasthowever, provide a dimensional stability of the part which, in somecases, reduces the amount of after-processing needed finish a part orthe number of dimensionally inaccurate parts.

Prior to operating the apparatus, a 3D solid computer model of thedesired part is sliced into virtual layers and saved into an electronicfile (not shown). This electronic file is then entered into the ComputerController 50 of the apparatus. At the start of operation of theapparatus, a set of commands from the Computer Controller 50 causes theBuild Table 5 to be initially positioned in or above the quenchant Level15 and the Robotic Actuator System 20 and the Z Axis Actuator 21 toposition the Deposition Nozzle Module 30 at a starting point and apredetermined optimum distance above the Build Table 5. The Enclosure 40is optionally filled at this time with the Inert Gas 36, by turning onthe flow or re-introducing gas which was saved from previous runs.

After checking and confirming that the environment within the Enclosure40 is being maintained at proper operating conditions by way of theoxygen sensor 48, the Computer Controller 50 turns on the DepositionPower Supply 35 and the flow of the Inert Gas 36. Feed wire is deliveredto the nozzle and an arc is struck. The first layer of the part isdeposited onto the Build Table 5 according to the profile in thesectioned 3D model file. Subsequent layers, as determined by the 3Dsolid computer model and the virtual layers thereof, are deposited toform a complete part.

The speed, power settings, and direction of the material deposition aredetermined by preloaded parameters within the Computer Controller 50.Since the temperature sensor 66 is mounted as part of the nozzle module30, the temperature sensor 66 is adjacent to the location of thedeposition of material, i.e. the deposition or hot zone, and records theinstantaneous temperature at a set distance from the deposition or hotzone. This data is received by the controller 50 and used in a computermodeling of an overall part temperature. For example, upon completion ofa layer, the average temperature of an aluminum part is read usingreadings from the temperature sensor 66 and the Build Table 5 is loweredor raised to cool or heat the part to a desired temperature prior tomoving on to deposition of the next layer. The build can be delayed orslowed down if the part is not within an acceptable temperature range,and thus ensure one or more of: 1) proper bonding between layers, 2)prevention or reduction of part sagging from addition heat input, 3)obtaining the desired material grain structure, and 4) achieving desiredphysical properties. Also, under the right conditions, the build iscontinuous and includes one, homogeneous material including thetransition from layer to layer. Travel speed control is, therefore, anadditional parameter which, can be used to control part temperatures. Asis known in the art, distortion control in forgings, castings and thinsheet metal parts as well as minimal residual stresses in forgings andcastings can be achieved by hot water quenching using hot water orwater/polyalkalene glycol mixtures.

Movement of the build table 5 is combined with movement in the Z axis ofthe Z Axis Rod 25 and is controlled by the controller 50 to vary thedistance between the quenchant and the hot zone of the part whilekeeping the deposition parameters constant. Therefore, the distancebetween the hot zone and the quenchant level 15 and the portion of thepart submerged, is continuously varied based on instantaneoustemperature readings, or is varied based on a model of overall parttemperature and varied in discrete steps as desired.

The temperature of the part as measured by the small single pointtemperature sensor 66 is received by the controller 50 and is used todetermine an average temperature over time, as the nozzle assembly 63moves along the path to deposit the material. In this embodiment, a linecan also be used for the temperature sensor, to achieve some mechanicalaveraging of the signal sent to the controller. In either case, thecontroller 50 is configured to use the received temperature values toaverage the temperature over time as would be understood by thoseskilled in the art.

During the deposition of each subsequent layer, the Z Axis Actuator 21positions the Deposition Nozzle Module 30 at a predetermined height fromthe top of the part, as predetermined by previous experimental testingof the apparatus. The Electronic height gauge 67 determines if any areasof the part are lower than desired. In another mode of operation, thearc provided by the nozzle assembly 63 is used to obtain a localizedvisual reference point corresponding to the height of the part beingformed.

The build is correctable by going back over the low sections, changingspeed and deposition parameters, or aborting the process if the partheight or position is found to be out of an acceptable tolerance.

Note that it is envisioned that the X-Y starting point for each layer,is moved slightly relative to a previous starting point of the previouslayer, so that there is minimal effect from the transient depositionduring arc start up. Furthermore, material deposition proceeds along acontinuous path without interruption to minimize the number of startingpoints.

In an alternate operating mode, the use of an analysis of depositionvoltages, currents, and other deposition supply characteristics whichare affected by the deposition process, are used to monitor height.Common in the welding industry is the use of voltage monitoring todetermine arc length and “stick out” which is the length of wireprotruding from a MIG nozzle during a welding operation. With a knowndistance for arc length, a known Deposition Nozzle Z axis position, anda known “stick-out”, dynamic determination of material height in thedeposition zone is a simple subtraction operation. This result is thenbe used to control the deposition rate, robotic motion speed, andmaintain optimal build height either in conjunction with height sensor66 and other sensors or as a standalone control.

In the preferred embodiment of the present invention, the wire used informing the part is a standard MIG welding wire but having a reducedamount of silicon. A typical silicon concentration for a currentlyavailable E70 MIG wire is in the range of 0.5-0.9% SI. In a preferredembodiment for use herein, the feedstock wire includes a silicon levelof approximately 0.2% or below SI.

Given that the Inert Gas 36 is typically heavier than air, the inert gas36 tends to sink to the bottom of the Enclosure 40. The Inert Gas Level46 is continuously monitored so that the deposition process is alwaysperformed in an inert gas environment. Furthermore, monitoring of other,undesirable gases, such as hydrogen near the deposition site, isperformed to help ensure optimum conditions for the metal depositionprocess. In this way, porosity, material embrittlement, and otherdeposition flaws are reduced or avoided resulting in a part that has thedesired mechanical properties.

Once the last layer is deposited and the part is therefore completed,the inert gas is purged from the enclosed space with the Vent Fan 47 andthrough a filter to clean the air of undesirable fumes. The DepositionNozzle Module 30 is moved out of the way by the Robotic Actuator System20 and the build table 5 is raised out of the quenchant 10 to allow thepart to be unloaded from the apparatus. At least one door in theenclosure 40 provides access to remove the completed part.

FIG. 4 illustrates the optional use of two MIG Welding Nozzles 91 torapidly deposit metal without the need for a conductive Build Table 5.Either an AC waveform or DC− polarity is provided by one Large Feed Wire92 and DC+ polarity is provided by another Small Feed Wire 93. In one ormore embodiments, other combinations of waveforms optimized to achievethe preferred semi-molten state of the Large Feed Wire 92 are provided.The size of the wires and the relative speed of the wire feeds are setin conjunction with the waveforms, voltages, currents and polarities sothat the Small Feed Wire 93 softens the Large Feed Wire 92 but does notcompletely melt it to the “droplet” stage. Thus, the Large Feed Wire 92is then able to be laid down in a semi-molten state to make the firstpass, with no need for conduction through the Build Table 5. After thefirst layer is deposited, the waveforms are switched so that one or bothof the wires produces fully molten droplets on the subsequent passes inorder to help minimize the heat input to the part and to optimizebonding and other deposition qualities.

Varying the heat input and the quenching affects the material propertiesin the deposited material, as well as providing control over warpagetendencies. As depicted, the deposition nozzles are angled towards eachother so that the Large Feed Wire 92 and Small Feed Wire 93 intersect ata convenient distance above the build table 5. Practitioners in the artwill readily recognize that the relationship between an included anglebetween the deposition nozzles and the height above the build table 5allows for variations in order to achieve optimum results and either orboth angles are varied as needed.

FIG. 5 illustrates an alternate embodiment which substitutes anon-consumable TIG Electrode 100 for the Small Feed Wire 93 in the aboveembodiment, such as is commonly used in Tungsten Inert Gas (TIG)welding. In this embodiment, the TIG Electrode 100 is used to soften theLarge Feed Wire 92 to allow deposition of the material, allowingswitching of current between the TIG Electrode 100, the MIG Large FeedWire 92, and the Build Table 5 if a metallic build table surface isused. This allows controlling the initial deposition as well assubsequent passes by using suitable configurations of currents for eachpurpose.

It should be understood that a combination of a Large Feed Wire 92, asmaller wire and a TIG electrode, or more than one wire of equal ordifferent diameters might be used to practice the invention, or that asingle wire with a TIG Electrode 100 might be used to deposit materialonto the Build Table 5 as initially described herein in lieu of feedingcurrent through the feed wire and using a typical MIG process.

In the preferred embodiment, regardless of the type of nozzle or nozzlesinstalled, the size of the feedstock wire and the relative speed of thewire feeds are determined in conjunction with the waveforms, voltages,polarity, and currents to be used by the deposition nozzles. It shouldbe noted that the first pass requires different settings than subsequentpasses and on subsequent passes after the first pass, the configurationand parameters are such as to create some localized heating of theformerly deposited layer in the deposition zone, either by current flowor by proximity such that acceptable bonding is achieved.

FIG. 6 illustrates the preferred embodiment of the fabrication system 1including a build table 102 disposed within a tank 104. The tank 104 isfilled with a quenchant and the build table 102 is lowered into the tank104 by supports 106, as previously described. In this embodiment, thebuild table 102 includes a frame 108 which defines a planar supportplane. The frame 108 includes a plurality of cutouts 110, each of whichis configured to accommodate a removable platen 112 having a buildsurface 114. The build surface 114 includes non-stick deposition surfaceincluding a high-temperature-resistant flat plate 116 which provides asmooth flat plane for the molten and semi molten material beingdeposited. The flat plate 116 includes a sufficient thickness configuredto provide the necessary strength to support the part being fabricated.The shape and size thereof is sufficient to avoid warping when subjectedto the heat of deposition. In the preferred embodiment the flat plate116 includes a copper or a copper alloy.

As can be seen in FIG. 6, each of the cutouts 110 is formed in the frame108 with crosspieces 118 of appropriate shape to receive one of theplatens 112, wherein one or more edges 120 abut an edge 120 of anadjacently located platen 112. In the preferred embodiment, the adjacentedges 120 form a seam that is sufficiently narrow to substantiallyprevent the heated material from entering the gap between the adjoiningplatens 112. While a table 102 having twelve cutouts 110 is illustrated,the present disclosure is not limited to a table 102 having twelvecutouts, and more or less cutouts of varying sizes are possible.

As seen in FIG. 6 and FIG. 7, platens 112 include a flat plate 116.Fixedly attached to the underside surface of the flat plate 116 is aplurality of heat dissipating fins 122. Each of the fins includes alength sufficient be in contact with the quenchant 10 and in sufficientquantity to draw the heat from the flat plate 116 and to dissipate theheat into the quenchant 10. The length of the fins 122, extending fromthe underside surface of the flat plate 116, is such that when the buildtable 102 is in the uppermost position, the ends of the fins 124 areimmersed in the quenchant 10. In this manner, the quenchant 10 is belowthe surface 114 of each of the flat plates 116 and does not interferewith the deposition. The number and length of the fins 124 can vary andstill achieve the desired heat transfer.

As further illustrated in FIG. 7, the plate includes an engaging portion126, which in the disclosed embodiment, is formed as part of the finstructure. Different engaging structures are possible. The engagingportion defines a channel 128, between the flat plate 116 and theengaging portion 126, and is configured to receive a portion of theframe 108, which in the embodiment of FIG. 6 is a portion of one of thecrosspieces 118. In this way, each of the platens 112 is forced intomaintaining good electrical contact with the table 102 during theformation of a part to provide the electrical connection to strike andmaintain a consistent arc.

Referring again to FIG. 6, the tank 104 includes a back wall 130 havinga horizontally located rectangular aperture 132, also known as a weir,which provides for the overflow of quenchant through the aperture 132and into an overflow reservoir 134. The overflow reservoir 134 includesa capacity sufficient to collect overflow of quenchant as the table 102and the part being formed are lowered into the tank 104. The aperture132, therefore, provides precise fluid level control of the quenchantremaining in the tank 104. The quenchant in the overflow reservoir 134is cycled back into the tank for circulation and then pumped back intothe tank 104 when the build is complete.

A heat exchanger 135 includes a radiator 136, located at the back wall130, and a fluid exchange device 138, fluidically coupled to theradiator 136. The fluid exchange device 138 includes a pump whichcirculates a temperature controlled fluid, such as a refrigerant,through the radiator 136 thus cooling the quenchant located in the tank104. In the preferred embodiment a sensing device is immersed in thequenchant to determine the temperature of the quenchant. Eliminating theheat exchanger 135 and circulating the quenchant through the fluidexchange device is equivalent.

The fluid exchange device 138 is configured to adjust the temperature ofthe temperature controlled fluid moving through the radiator 136. Thetemperature of the quenchant 10 located in the tank 104 is therebyraised or lowered to provide a preferred temperature for controlling thetemperature of the part being formed. In this way, the build process isoptimized for providing usable parts having the desired properties.

FIG. 8 illustrates a portion of the platen 108 including the flat plate116 defining the surface 114. As described above, the surface 114includes a non-stick deposition surface which provides a smooth flatplane for the molten and semi molten material being deposited. Using thedeposition nozzle module 30 of FIG. 1 including the deposition nozzleassembly 63, a part is formed through the deposition of molten orsemi-molten metal or metal-like material at the surface 114. To beginthe formation of the part, a plurality of spots 140 of the material aredeposited at spaced locations on the surface 114. To deposit the spots140, the power supply 35 is adjusted to deliver a current to the nozzleassembly 63 which is sufficient to adhere the spots 140 to the surface114, in a relatively secure fashion, such that a metal bond is formedbetween the surface material and the deposited spot material. If theplate 116 is formed of copper, for instance, the power is adjustedsufficiently to break through the oxidation at the surface to providegood, consistent, electrical contact.

Each of the spots 140 includes a mound of material, which provides astable structure electrically connected to the plate 116 upon which theremainder of the part is formed. Once the spots 140 are deposited, abead of molten or semi-molten metal or metal like material 142 isdeposited between each of the spots 140 to connect one spot 140 to thenext spot 140 or alternatively over or next to the spots 140. In formingthe beads 142, the power of the power supply is adjusted to provide acurrent typically lower than the current used to form the spots 140. Inthis fashion, the beads 142 do not form a metal bond with the surface114, but do form a bond with the spots 140. Once a first layer 144 ofthe part, including spots 140 and beads 142 are formed, additionallayers 146 formed of continuous beads of material are deposited onpreviously formed layers, as described above. As a result, thedeposition nozzle assembly 63 does not act as a welder, but instead isused to merely melt the metal wire fed through the nozzle. The powerdoes not bond the metallic beads 142 to the no stick plate 116. Theapplication of the beads 142 are either continuous or segmented asillustrated and is varied depending on the spacing of the spots 140 andother parameters including sensed temperatures, material types, andspeed of deposition.

The part is easily removed from the build surface 114 by tapping thepart or the build surface or by the application of a minor impact forceto the part or build surface.

The power setting of the power supply 35 during the deposition of thebeads 142 and subsequent layers 146 is not at a level typically used ina metal to metal welding process, but is reduced from that level and isgenerally a fraction of that used in a typical welding process. In oneembodiment, the power level being used is approximately twenty fivepercent or less than the power typically required in a welding operationfor the same metal. The power supply setting can also be adjusted tovary the current or voltage used to form the layers in response to thetemperature being sensed by the temperature sensor 66. For instance, asadditional layers are formed, the temperature being sensed changes dueto part geometry and the power supply setting is adjusted accordingly.In the preferred embodiment, the polarity of the electrode of the nozzleassembly 63 is alternated from positive to negative depending on thelayer and material of deposition. To facilitate the change in polarity,a silicon controlled rectifier (SCR) is used within the wire feedcircuit of the nozzle assembly and build table to change polarity asnecessary.

The controller 50 is configured to control the application of thematerial being deposited by the nozzle module 30 during formation of apart. The controller includes one or more computer processors configuredto operate according to software based routines which are written toimplement the embodiments of the invention. Whether implemented as partof an operating system or a specific application, component, program,object, module or sequence of instructions the software routines arehereafter referred to herein as “computer program code”, or simply“program code”. The computer program code typically comprises one ormore instructions that are resident at various times in various memoryand storage devices in the controller, and that, when read and executedby one or more processors in the controller, causes the roboticactuators, welding power supply, and chilling device to perform thesteps necessary to execute formation of the object or parts.

In addition, it should be appreciated that the method or methodsdescribed herein are implementable in various program code and shouldnot be limited to specific types of program code or specificorganizations of such program code. Additionally, in view of thetypically endless number of manners in which computer programs may beorganized into routines, procedures, methods, modules, objects, and thelike, as well as the various manners in which program functionality maybe allocated among various software layers that are resident within acontroller or computer if used, (e.g., operating systems, libraries,APIs, applications, applets, etc.), it should be appreciated that theinvention is not limited to a specific organization.

The controller 50 and resident program code is configured to form a 3dimensional metallic part of any shape through the control of a numberof parameters and conditions including material temperatures, holdtimes, deposition speed, tool identification, and power settings of thepower supply to optimize deposition rates for a given layer of the part.In addition, as described herein different materials and different wiresizes can be used, either in a single nozzle assembly or in multiplenozzle assemblies which are changed by hand or automatically in thesystem 1. Weld parameters and temperature sensor emissivity is alsocontrollable for different materials.

FIG. 9 illustrates a side view of a preferred embodiment of a nozzlehead fixture 150 and a nozzle assembly 152. The nozzle head fixture 150is configured to engage a plurality of different nozzle assemblies 152,each of which is directed to forming a bead of material of a differenttype. For instance, a plurality of nozzle assemblies 152 are parked at adocking station (not shown) for intermittent use during the formation ofa part. One of the nozzle assemblies 152 is selected by the controller50, based on the type of material to be deposited, and that nozzleassembly 152 is picked by the nozzle head fixture 150 from theappropriate location of the docking station where the pick is made. Thenozzle head fixture 150 is coupled to the Z axis actuator 21 Z-rod 50 ofFIG. 1 which in turn is coupled to wrist actuator 156. The wristactuator 156 is configured to rotate the head fixture 150 about thez-axis defined by the z-rod 50. A temperature probe 160, such as thatpreviously described, is coupled to the nozzle head fixture 150 and isconfigured to sense the temperature of the product being formed. Inanother embodiment, each of the nozzle assemblies includes a temperatureprobe. A tool bracket 164 which is coupled to a torch portion 166 of thenozzle assembly 152. A nozzle head 167 extends below the tool bracket164. A flexible conduit 168 coupled to the torch portion 166 suppliesthe predetermined type of wire and gas. The master bracket 158 includesan aperture 170 configured to receive a portion of the tool bracket 164.As seen in FIG. 9, the tool bracket 164 includes a channel 172configured to hang the tool from the docking station or other storagerack when not in use. In the preferred embodiment, the storage rack islocated within the enclosure 40.

FIG. 10 illustrates a back view of the nozzle head fixture 150 and thenozzle assembly 152. The nozzle head fixture 150 is configured tosupport a position sensor 176.

FIG. 11 illustrates a front perspective view of the nozzle head fixture150 and the docked nozzle assembly 152. As can be seen, the beam of thetemperature sensor extends below the bottom edge of the tool bracket164.

FIG. 12 illustrates a perspective view of a part 180 being formed with apart build fixture 182. The part build fixture 182 is located adjacentlyto a side 184 of the part 180 and includes a non-stick surface 186 uponwhich a shelf 188 is formed by the deposition process. The part fixture182 provides support for the shelf 188 such that the shelf 188 extendsfrom the wall 184 in a cantilever and accurate fashion. Removal of thepart fixture 182, after completion of the part 180 leaves a space orvoid below the shelf 188. Additionally, a specially made form 190 of nonstick material is added to during formation, as needed, to provide adesired geometry to the finished part 180. Alternatively, cavities,elevated surfaces and smooth surfaces are similarly formed. The use ofsuch fixtures and forms provides for a more accurate control of thegeometric shapes, dimensional sizes and finishes of the objects beingformed. In the preferred embodiments, however, the formation ofoverhangs, arches and similar structures are formed without the use ofsupplemental supports. The formation of these types of structures areprovided with the addition of one additional axes of movement whichenables the nozzle to be angled upwards through an selectable andcontrolled angle of 90 degrees or more to enable the deposition ofmaterial in a horizontal direction, a direction angled from horizontal,or upwards from horizontal.

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed herein, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

I claim:
 1. An additive manufacturing apparatus for fabricating a threedimensional object comprising: a multi-axis robotic system configured tosupport and move a deposition head; the robotic system contained withina sealed enclosed space; an oxygen sensor within the enclosed space. 2.The additive manufacturing apparatus as set forth in claim 1 forfabricating a three dimensional object further comprising means forintroducing a gas and monitoring the oxygen concentration within theenclosed space.
 3. The additive manufacturing apparatus as set forth inclaim 2 further comprising a means for reducing or discontinuing gasflow in response to said oxygen monitoring.
 4. The additivemanufacturing apparatus as set forth in claim 1 further comprising anair filtration system.
 5. An additive manufacturing apparatus tofabricate objects by depositing metal or metal like materials in threedimensions comprising: a build table; a deposition head configured todeposit the metal objects on the build table; a multi-axis roboticsystem configured to support the deposition head; wherein said buildtable is configured to be adjustably located in a tank, said tank havinga quenching fluid therein; wherein material is deposited at a setdistance from the level of the quenchant.
 6. The additive manufacturingapparatus as set forth in claim 5 wherein said deposition head iscapable of being fully submerged in said quenchant.
 7. The additivemanufacturing apparatus of claim 6 further comprising use of wire withinternal inert gas filler.
 8. An additive manufacturing apparatus tofabricate objects by depositing metal or metal like materials in threedimensions comprising: a build table; a plurality of deposition headsconfigured to deposit the metal objects on the build table, wherein eachof the deposition heads includes a tool bracket; a multi-axis roboticsystem configured to support the deposition head; wherein said buildtable is configured to be adjustably located in a tank, said tank havinga quenching fluid therein; wherein the plurality of nozzle assembliesare configured to deposit different wire sizes of metal or metal-likematerial.
 9. The method of claim 8 further comprising each of theplurality of deposition heads configured to deposit a differentmaterial.
 10. The method of claim 8 further comprising one welding powersupply and changing computer control programs for each deposition head.11. The method of claim 10 further comprising using switchable powerbuss to provide power to each of said multiple deposition heads.
 12. Anadditive manufacturing method for fabricating a three dimensional objectformed from a metal or metal-like material, wherein the geometry andtemperature of the object is continually monitored and deviations fromthe desired geometry or temperature are corrected prior to continuing.13. The additive manufacturing method of claim 12 further comprisingusing the arc current to continually monitor the height of the object.14. The additive manufacturing method as set forth in claim 12 furthercomprising using a computer control program capable of depositing one ormore layers using one power setting alternated with one or more layersdeposited using a second power setting.
 15. The additive manufacturingmethod of claim 12 further comprising using a computer control programto correct defects by moving the deposition head back over low sectionsprior to proceeding with the next layer.
 16. The additive manufacturingmethod as set forth in claim 15 further comprising using a computercontrol program to correct surface defects by changing the robotictravel speed, and by changing the deposition parameters of the nextlayer when reaching the location of the detected defect.
 17. Theadditive manufacturing method of claim 16 further comprising the step ofusing a computer control to abort the build process prior to completionof the object.
 18. The additive manufacturing method of as set forth inclaim 17 further comprising using a memory storage device and recordingall locations of any detected defects for later analysis.
 19. The methodof claim 18 further comprising creating a visual display of thelocations of any detected defects.